diff --git a/substrate/client/db/src/utils.rs b/substrate/client/db/src/utils.rs
index f7f51d7f6d..534cbb2197 100644
--- a/substrate/client/db/src/utils.rs
+++ b/substrate/client/db/src/utils.rs
@@ -320,7 +320,9 @@ pub fn require_header<Block: BlockT>(
 	id: BlockId<Block>,
 ) -> sp_blockchain::Result<Block::Header> {
 	read_header(db, col_index, col, id)
-		.and_then(|header| header.ok_or_else(|| sp_blockchain::Error::UnknownBlock(format!("{}", id))))
+		.and_then(|header| header.ok_or_else(||
+			sp_blockchain::Error::UnknownBlock(format!("Require header: {}", id))
+		))
 }
 
 /// Read meta from the database.
diff --git a/substrate/client/offchain/src/lib.rs b/substrate/client/offchain/src/lib.rs
index f0a10a5409..fadfaa0134 100644
--- a/substrate/client/offchain/src/lib.rs
+++ b/substrate/client/offchain/src/lib.rs
@@ -97,7 +97,7 @@ impl<Client, Storage, Block> OffchainWorkers<
 		is_validator: bool,
 	) -> impl Future<Output = ()> {
 		let runtime = self.client.runtime_api();
-		let at = BlockId::number(*header.number());
+		let at = BlockId::hash(header.hash());
 		let has_api_v1 = runtime.has_api_with::<dyn OffchainWorkerApi<Block, Error = ()>, _>(
 			&at, |v| v == 1
 		);
@@ -169,7 +169,6 @@ mod tests {
 	use substrate_test_runtime_client::runtime::Block;
 	use sc_transaction_pool::{BasicPool, FullChainApi};
 	use sp_transaction_pool::{TransactionPool, InPoolTransaction};
-	use sp_runtime::{generic::Header, traits::Header as _};
 
 	struct MockNetworkStateInfo();
 
@@ -210,13 +209,7 @@ mod tests {
 			.register_transaction_pool(Arc::downgrade(&pool.clone()) as _);
 		let db = sc_client_db::offchain::LocalStorage::new_test();
 		let network_state = Arc::new(MockNetworkStateInfo());
-		let header = Header::new(
-			0u64,
-			Default::default(),
-			Default::default(),
-			Default::default(),
-			Default::default(),
-		);
+		let header = client.header(&BlockId::number(0)).unwrap().unwrap();
 
 		// when
 		let offchain = OffchainWorkers::new(client, db);
diff --git a/substrate/client/service/src/builder.rs b/substrate/client/service/src/builder.rs
index 4d672006b8..e29c503402 100644
--- a/substrate/client/service/src/builder.rs
+++ b/substrate/client/service/src/builder.rs
@@ -898,16 +898,24 @@ ServiceBuilder<
 					}
 
 					let offchain = offchain.as_ref().and_then(|o| o.upgrade());
-					if let Some(offchain) = offchain {
-						let future = offchain.on_block_imported(
-							&notification.header,
-							network_state_info.clone(),
-							is_validator
-						);
-						let _ = to_spawn_tx_.unbounded_send((
-							Box::pin(future),
-							From::from("offchain-on-block")
-						));
+					match offchain {
+						Some(offchain) if notification.is_new_best => {
+							let future = offchain.on_block_imported(
+								&notification.header,
+								network_state_info.clone(),
+								is_validator,
+							);
+							let _ = to_spawn_tx_.unbounded_send((
+									Box::pin(future),
+									From::from("offchain-on-block"),
+							));
+						},
+						Some(_) => log::debug!(
+							target: "sc_offchain",
+							"Skipping offchain workers for non-canon block: {:?}",
+							notification.header,
+						),
+						_ => {},
 					}
 
 					ready(())
diff --git a/substrate/primitives/blockchain/src/backend.rs b/substrate/primitives/blockchain/src/backend.rs
index 101dcd1443..35cac1e481 100644
--- a/substrate/primitives/blockchain/src/backend.rs
+++ b/substrate/primitives/blockchain/src/backend.rs
@@ -59,19 +59,23 @@ pub trait HeaderBackend<Block: BlockT>: Send + Sync {
 
 	/// Get block header. Returns `UnknownBlock` error if block is not found.
 	fn expect_header(&self, id: BlockId<Block>) -> Result<Block::Header> {
-		self.header(id)?.ok_or_else(|| Error::UnknownBlock(format!("{}", id)))
+		self.header(id)?.ok_or_else(|| Error::UnknownBlock(format!("Expect header: {}", id)))
 	}
 
 	/// Convert an arbitrary block ID into a block number. Returns `UnknownBlock` error if block is not found.
 	fn expect_block_number_from_id(&self, id: &BlockId<Block>) -> Result<NumberFor<Block>> {
 		self.block_number_from_id(id)
-			.and_then(|n| n.ok_or_else(|| Error::UnknownBlock(format!("{}", id))))
+			.and_then(|n| n.ok_or_else(||
+				Error::UnknownBlock(format!("Expect block number from id: {}", id))
+			))
 	}
 
 	/// Convert an arbitrary block ID into a block hash. Returns `UnknownBlock` error if block is not found.
 	fn expect_block_hash_from_id(&self, id: &BlockId<Block>) -> Result<Block::Hash> {
 		self.block_hash_from_id(id)
-			.and_then(|n| n.ok_or_else(|| Error::UnknownBlock(format!("{}", id))))
+			.and_then(|n| n.ok_or_else(||
+				Error::UnknownBlock(format!("Expect block hash from id: {}", id))
+			))
 	}
 }